You Can Maybe Blame Antibiotics for Making You Gain Weight

Animal antibiotics are a hot topic among people interested in agricultural policy or public health (or those who’ve watched Food Inc.). The general public? Not so much. But according to a recent feature in The Atlantic, all that might change as experts tease out the connection between antibiotic overuse and our expanding guts.

The backstory: Ranchers and farmers routinely give their animals antibiotics to help prevent infection, rather than to treat existing illness. Such widespread use is frowned upon in the interest of preventing deadly antibiotic-resistant superbugs, and companies including Chipotle and Whole Foods have publicly shunned animal products raised with antibiotics. But the drugs also stimulate animals’ appetite and growth, and ranchers have been known to use antibiotics to make livestock larger. Now, experts believe the drugs given to animals could be making us fatter, too.

It has to do with our microbiome, the complex ecosystem of bugs in our bodies, which is the subject of a new exhibit at the American Museum of Natural History called “The Secret World Inside You.” We know that antibiotics can disrupt this system — think of doctors who write you that prescription and suggest eating yogurt to help prevent diarrhea or yeast infections — but more and more research has shown that changes in people’s intestinal microbes can also lead to changes in weight. (The gut-scale connection is not new: Experts think the microbiome could help us understand human metabolism and researchers are already developing a diet algorithm based on people’s gut microbes.)

Even if you’re not the type to run to your doc for a Z-pack and you only buy organic meat and dairy, you might still come into contact with the drugs, since livestock excrete them and they make their way into our soil and water. To wit, antibiotics have been detected in produce like lettuce, carrots, and green onions.

The Atlantic reports that, in 2014, nearly 34 million pounds of antibiotics were sold for use in U.S. food animals, up 22 percent from 2009. (A whopping 70 percent of antibiotics in this country go to farm animals, per the AMNH exhibit.) The FDA wants that number to shrink, but thus far, they’ve only called on the industry not to use them as growth promoters. It’s still okay to use them to prevent infection.

Lee Riley, chair of the division of infectious diseases and vaccinology at the University of California, Berkeley, told The Atlantic that we, the consumer, will have to fuel the revolution: “You have two of the strongest lobbies in the world — the pharmaceutical industry and the food industry — so change is just not going to come from our government. But if people really recognize that the obesity epidemic is associated with exposure to antibiotics, I think demand for antibiotic-free food will become even greater.”

Which leaves us with two options: Go vegetarian until we live in an antibiotic-free utopia, or just relish the fact that we now have a new scapegoat for those extra pounds.